For more matter & energy stories,visit www.sciencenews.orgDiamond may have a softer cousin

By Devin Powell

Diamond may have a softer side:
T-carbon.

This fluffy form of diamond, simulated in a Chinese supercomputer, could
be used for a variety of applications — if
someone can make the
stuff and prove that it is
stable in the real world.

“What is the most surprising to us is that such
an elegant structure has
never been proposed
before,” says Gang Su, a
materials scientist at the
Graduate University of
the Chinese Academy of
Sciences in Beijing and a
coauthor of an upcoming paper describing T-carbon in Physical Review Letters.

Inspired by a television show aboutEgypt’s pyramids, Su calculated how torevamp the crystal structure of cubic dia-mond by exchanging each carbon atomwith a pyramid of four carbon atoms. Thisarrangement should be 43 percent asdense and 65 percent as hard as diamond.

“It would be a very light, hard material,
so you could imagine a large number of
applications,” says Wendy Mao, a geophysicist at Stanford University who was
not involved with the research.

Su and colleagues hope the material
would be valuable for
the aerospace industry
and for storing hydrogen.
Because of the way electrons would flow through
T-carbon, it could also be
useful as a semiconductor.
The researchers speculate that T-carbon may be
found in interstellar dust,
helping explain distortions of light in the dust
noticed by astronomers in 1965.

But other physicists doubt that these
carbon pyramids will ever be built.
Because of carbon’s remarkable ability to
form different kinds of molecular bonds,
there are countless ways carbon atoms can
be rearranged to form new structures, says
crystallographer Artem Oganov of Stony

Replacing diamond’satoms with pyramids ofcarbon could produce anew form of carbon.

Brook University in New York. Most such
arrangements, though, are too unstable
to exist in an everyday environment. The
trick is to find the few that can actually
be created and stick around, thus joining
the family of carbon “allotropes,” which
includes graphite and amorphous carbons
such as soot ( both found in nature) as well
as lab-produced substances such as gra-phene, carbon nanotubes and fullerenes.

“I think there will be problems in synthesizing” T-carbon, says Oganov.

Because of T-carbon’s low density, it
must be formed at pressures far below
atmospheric levels. Other recent efforts
to make new forms of carbon have
focused on generating high pressures by
squeezing materials. To make T-carbon,
Su proposes detonating a chunk of diamond or graphite, or creating negative
pressures “somehow by stretching diamond with an extremely large strength.”
Renata Wentzcovitch, a materials scientist at the University of Minnesota in Minneapolis, says that even if T-carbon was
synthesized, “I don’t know if it would hold
together.” Lower-energy structures tend
to be more stable. “The energy of this stuff
is much, much higher than other forms of
carbon,” she says, “and little perturbations
might cause the structure to collapse.” s

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useful for optical devices. — Devin Powell